The present invention relates to a method and a system for controlling active suspensions of a vehicle.
A known active suspension system of a vehicle comprises suspensions into and out of which a fluid is charged and discharged independently to maintain a reference vehicle height by extending and contracting the suspensions responsive to vertical relative displacements between the wheels and the vehicle body at the positions of the respective suspensions.
Japanese Patent Application Laid-Open Pub. No. 2-95,911 discloses an active suspension system as described above wherein there are provided a longitudinal G-sensor for detecting longitudinal acceleration being applied to the vehicle and a lateral G-sensor for detecting lateral acceleration being applied to the vehicle. In the system, the degrees of pitching and rolling of the vehicle are preestimated responsive to the longitudinal and lateral accelerations detected during acceleration, deceleration and turning of the vehicl. The prestimation is performed by charging and discharging quantities of fluid into and out of the respective suspensions to suppress pitching and rolling of the vehicle.
Japanese Patent Application Laid-Open Pub. No. 2-124,310 discloses an active suspension system as described above, wherein there is further provided a switch for selecting the direction and degree of rolling of the vehicle during a turn thereof. In the system, the charging and discharging of the fluid into and out of the respective suspensions are so controlled as to keep the vehicle at an optimum rolling angle based upon the lateral acceleration and the selected direction and the degree of rolling.
The active suspension systems described above have a feed back control system for controlling the suspensions so as to maintain a reference vehicle height responsive to relative vertical displacements between the respective wheels and the vehicle body. The active suspension systems have, in addition to the feed back control system, a feed forward control system for maintaining preestimated vehicle rolling and pitching responsive to longitudinal and lateral accelerations detected during vehicle acceleration, deceleration and turning. By combining the feed forward control system with the feed back control system, the attitude of the vehicle is maintained at a desired attitude without delay.
However, the known active suspension systems described above have a disadvantage in that the driver is caused to feel an unnatural feeling or sensation of being pressed from the forward side because contraction of the suspension of the outer wheel is set to be very small or zero.